Conventional plastics are polymers made from monomeric materials derived from non-renewable petroleum and/or natural gas (petroleum-based-plastics or p-plastics). The identity of the particular plastic is characterized by the component monomers. Common plastics include, for example, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS), nylon, polycarbonate (PC), polyvinyl chloride (PVC), etc. PET is formed primarily from monoethylene glycol (MEG) and terephthalic acid (TA) (Scheme 1) and is widely used in bottles and containers for food and beverage products.

Non-renewable petroleum-based plastics have come under scrutiny for their environmental profile, including their role in contributing to greenhouse emissions and their “non-renewable” nature, meaning that they cannot be re-made, re-grown, or regenerated at a rate comparable to consumption. Non-renewable petroleum is made from oil which takes millions of years to form. The cost of non-renewable petroleum-derived plastics, which is closely tied to the rising cost of non-renewable petroleum, has also proven to be a negative for many users.
The problems posed by traditional plastics have led to the search for alternative materials. Renewable bio-based plastics or renewable bioplastics represent a new class of plastics made from renewable bio-mass source materials. These materials may include food or non-food crops including, for example, corn, rice, soy, or other sugar and starch-producing plants. A given plastic may be formed partially or fully from renewable bio-derived materials. Renewable bio-based PET, for example, can be made from renewable bio-derived monoethylene glycol (b-MEG) and non-renewable petroleum-derived terephthalic acid (p-TA). As a group, renewable bioplastics offer environmental advantages compared to non-renewable petroleum-based plastics, including a more limited reduced impact of greenhouse gas emissions and renewability.
Renewable bio-based plastics, such as renewable bio-based PET, can be produced using the existing manufacturing technology, more often than not using the same reactors and machinery. As a producer transitions from manufacturing petroleum-based plastics to renewable bioplastics, the non-renewable petroleum-derived starting materials are replaced with renewable bio-derived starting materials (or visa versa). During the transition, a mix of non-renewable petroleum-derived and renewable bio-derived materials are present. This mixing leads to the need for measuring renewable bio-content of the renewable bioplastic product.
Any product that contains some amount of renewable bio-based material within it is technically a renewable bio-based product. However, a certain minimum renewable bio-content is characteristic of materials labeled as renewable bio-plastics. A renewable bio-based PET resin made of renewable bio-derived monoethylene glycol (renewable bio-MEG) and non-renewable petroleum-derived terephthalic acid (p-TA) may contain up to about 30% renewable bio-content.
It is possible to determine the amount of carbon in a product that is derived from renewable bio-based materials relative to the total amount of carbon in the entire product. This is because renewable biomass contains a well-characterized amount of carbon-14 that is easily differentiated from other materials, such as fossil fuels, that do not contain any carbon-14. The percentage of a given product that is derived from renewable bio-based materials is generally measured by Accelerator Mass Spectrometry (AMS) or Liquid Scintillation Counters (LSC). LSC is generally considered relatively low precision and requires extensive sample preparation as well as long counting times that can take from days to weeks. AMS provides higher precision, but the capital and operating costs are high. In addition, processing time for third party vendor analysis of AMS can be long.
Thus, there is a need for a method to measure the renewable bio-source carbon content of a renewable bioplastic resin manufactured in a production facility efficiently and cost-effectively. In particular, in order to optimize the manufacturing process such that the maximum amount of renewable bio-material can be produced; there is a need to quickly and reliably measure the renewable bio-source carbon content of a renewable bioplastic resin manufactured in a production facility over time, particularly during transition periods in the process where non-renewable petroleum-derived plastic starting materials are swapped out for renewable bio-derived plastic starting materials.
Other objects, features, and advantages of this invention will be apparent from the following detailed description, drawings, and claims.